1. Field of the Invention
The present invention pertains to calibration references for use with optical wavelength measuring devices such as Optical Spectrum Analyzers. In particular it pertains to calibration references using broad band light sources coupled to gas cells providing absorption lines at known wavelengths, and methods for using them.
2. Art Background
Optical wavelength measuring devices such as Optical Spectrum Analyzers are complex eletromechanical systems. Periodic calibration is required to maintain the accuracy of such systems. To perform such calibration, references are used. A reference may be emissive, providing energy at a known wavelength or frequency, or group of wavelengths or frequencies, or it may be absorptive, coupled to a broadband source and providing absorption lines at known wavelengths or frequencies. It is understood that wavelength and frequency are reciprocals, and may be interchanged.
To be suitable as a reference, the device in question should provide a stable output in varying environmental conditions, such as temperature, humidity, and atmospheric pressure. The device must also provide a stable reference over long periods of time. The other requirement for a reference is that it cover the frequency or wavelength range of interest. References based on mechanical properties can be manufactured, but they are typically bulky, and require initial calibration and periodic recalibration, typically at the factory.
Modern optical communications systems have extended from wavelengths in the 1.5 micrometer region to the 1.6 micrometer region. What is needed is a reference which covers both the 1.5 and 1.6 micrometer regions, and one which remains stable over time.